Inhibition of elongation factor 2-dependent translocation by the pokeweed antiviral protein and ricin.

The pokeweed antiviral protein and the toxin ricin are two plant proteins which enzymatically inactivate eukaryotic ribosomes and cause the inhibition of the elongation cycle of protein synthesis. Their mode of inhibition of protein synthesis has been attributed to either the inhibition of enzymatic binding of aminoacyl-tRNA to the acceptor site of the ribosome or its subsequent translocation to the donor site. In this communication, we show that the treatment of ribosomes with either the pokeweed antiviral protein or ricin results in the inhibition of the elongation factor 2-catalyzed translocation of acceptor site aminoacyl-tRNA to the donor site. The inhibitory effects of both proteins are identical and are partially reversed by excess concentrations of elongation factor 2.